Artificial insemination (AI), along with in vitro fertilization and embryo transplantation, afford enhanced reproduction in mammals, including livestock, and offer many advantages over direct mating. In the livestock breeding art, these techniques permit wider dissemination of desirable genetic features. Semen collected from a single male can be used to inseminate multiple females, thereby reducing the number of males required to maintain a population. Artificial insemination techniques permit greater control over breeding, which results in greater reproducibility and facilitates maintenance of large-scale operations.
Maintaining the viability of reproductive cells is an important aspect of artificial insemination and other techniques used in indirect breeding. The processing requirements for semen used in AI may vary according to the species of animal. Bovine insemination requires relatively low concentrations of semen, and a suitable sample may be rapidly frozen in a narrow diameter straw and stored for an extended period of time without adversely affecting the fertility of the sample. In contrast, porcine semen is not susceptible to this approach, because greater numbers of sperm cells and larger volumes of semen or diluted semen are required to inseminate sows. Insemination using frozen boar semen has not been sufficiently satisfactory to justify widespread use of this technique. Boar semen is generally diluted or extended with a suitable storage medium and cooled to a temperature of about 17° C. prior to transport. The culture medium serves to increase the total volume of the sample and provide nutrients to maintain the sperm cells. Significant loss of sperm cell vitality occurs after storing the semen for just a few days. Currently, the best medium generally maintains boar sperm cell viability for about five to seven days. The relatively short time that boar semen can be stored imposes considerable constraints on the distribution of boar semen for AI. Other animals, such as horses, produce sperm cells that also suffer from short-lived viability.
Artificial insemination, in vitro fertilization, and embryo transfer technology are also used in humans to aid in the conception process, and/or as a solution to various physiological problems relating to infertility. Clearly, maintaining the viability of reproductive cells for these uses is also very important.